1. Field of the Invention
The present invention relates to an electroless metal film-plating system in which, while a roll of film (polyimide film) is continuously fed, one or both surfaces thereof are plated with conductive metal in a wetting manner. More particularly, the present invention relates to an electroless metal film-plating system in which, while polyimide film is continuously fed from a roll, a series of wetting process, including a degreasing process, an etching process, a neutralizing process, a coupling process, a catalyst-adding process, an electroless undercoating process, and a plating process, are conducted, in order, so as to plate one or both surfaces of the film with conductive metal, followed by drying the conductive metal-plated film and taking up the plated film into a roll.
2. Description of the Prior Art
A conductive metal-plated film (e.g., polyimide film), of which a flexible copper clad laminate (hereinafter referred to as “FCCL”) is representative, is the most essential for flexible Printed Circuits (hereinafter referred to as “FPCs”).
In FPCs, generally, a polyester, a polyimide, a liquid crystal polymer, or a fluorine resin film is employed as an insulating film, with a polyimide film being preferred due to its superiority in thermal resistance, dimensional stability and solderability.
A conductive metallic material suitable to be layered on the insulation film (polyimide film) should be low in electrical resistance and show high conductivity, and examples thereof include gold and copper, with preference for copper due to its low cost.
FCCL, comprising a polyimide film and a conductive metal film (copper thin film) layered thereon, may be largely divided into two types: a trilayer structure consisting of a polyimide film, an adhesive layer, and a conductive metal film (copper); and a bilayer structure consisting of a polyimide film and a conductive metal film (copper).
However, the trilayer structure FCCL does not allow the formation of fine patterns without great difficulty and is also poor in flexibility. In addition, the low thermal resistance of the adhesive layer prohibits the execution of high-temperature processes such as soldering. For these reasons, the bilayer structure FCCL is preferred.
For the fabrication of FCCL, laminating, casting or plating methods are current used.
In a laminating method, liquid polyimide as an adhesive is applied to a polyimide film and fixed thereon by heating in oven, and a copper thin film is placed on the adhesive and pressed against the adhesive to fabricate an FCCL.
A casting method comprises layering liquid polyimide on a copper thin film and casting the resulting structure to afford an FCCL.
As for a plating method, it is conducted in a plating condition for forming a copper layer on a polyimide film.
Of these FCCL fabricating methods, the laminating method and the casting method are problematic in that uses for polyimide films and adhesives are limited.
In contrast, the plating method enjoys the advantages of needing no commercialized copper thin films and being able to control the thickness of copper thin film upon plating.
However, the FCCL fabricated by conventional plating methods exhibits relatively poor physical properties, such as peel strength, than does that fabricated by other methods. Therefore, there is an urgent need for a conductive metal-plated polyimide film, such as FCCL, that is greatly improved in physical properties including peel strength.
Generally, a rotating roller installed in a fabrication apparatus of FCCL has a cylindrical roller portion whose surface is made from rubber, with an axis inserted at the center thereof.
As driving rollers operate, conveying rollers are rotated to transport a target to be processed, such as a film.
For example, when a conveying roller rotates at a speed of 310 rpm, the film is conveyed while being in close contact with the roller. During rotation, heat is generated in the roller due to friction, resulting in an increase in the surface temperature of the roller.
Hence, the film in close contact with the roller may be temporarily adhered to the roller due to the heat or pressure of the roller, so that it cannot proceed, but turns together with the conveying roller. As a result, the film is rolled until it becomes tangled or broken.
When a film is conveyed by conventional rollers in liquid, it occasionally slips from the rollers because the liquid between the film and the rollers is insufficiently drained. In the case that rollers for conveying a film are submerged in liquid while they rotate, liquid is excluded from the surface of the rollers.
When a roller transports a film by rotation, a high coefficient of friction is generated between the film and the roller if it is dry. The existence of water between the film and the roller decreases the coefficient of friction because the water serves as a lubricant. If the rotation speed of the roller is increased without the proper draining of the liquid, the film is not directly contacted with the surface of the roller and undergoes hydroplaning. As a result, the film slips from the roller.
Therefore, where a roller rotates in liquid or with its surface wetted, the roller does not function properly because the film slips from the roller and is damaged.